There are many ways to apply a liquid saturant to a permeable sheet. For example, a saturant such as a dye solution may be applied to permeable sheets by a size press or dip/dunk and press process. Such processes may be unsatisfactory for some applications because the compressive forces involved may diminish sheet bulk and desirable properties associated with bulk. In addition, it may be difficult to achieve a uniform distribution of the saturant throughout the permeable sheet (e.g., throughout the interior of the permeable sheet).
Processes such as printing or spraying may also be used to apply a saturant such as a dye solution. Printing processes and spraying generally apply a saturant to a single surface of a sheet. Such processes may be unsatisfactory because they may create additional complexity if it is desired to apply a saturant to both sides of a sheet. Also, such processes may have difficulty achieving uniform distribution of the saturant throughout the permeable sheet.
Some types of permeable sheets are made by wet-forming processes. Liquid saturant may be applied to such sheets by adding saturant to the water used in the wet-forming process. Such a process may make relatively inefficient use of the saturant, especially if the process water is not properly recycled.
Thus, a need exists for a practical process for non-compressively and uniformly applying a liquid saturant throughout a permeable sheet. There is also a need for a practical process for non-compressively and uniformly applying a liquid saturant throughout a permeable fibrous cellulosic material. There is also a need for a practical apparatus for non-compressively and uniformly applying a liquid saturant throughout a permeable sheet.